The present invention relates to an apparatus for simultaneously sewing two coupled stringers of a slide fastener onto portions of a carrier to opposite sides of an elongated slit therein, and in which the carrier is elastic in the direction of the slit. In sewing operations it is often necessary to sew two coupled stringers of a slide fastener onto portions of a highly elastic material to opposite sides of an elongated slit therein in which the length of the slide fastener has to be determined in such a manner that this length corresponds with the length of the slit in tensioned condition of the carrier material. This problem arises for instance in series manufacturing of slip covers for upholstered furniture or the like. Thereby it is common practice to use for the slip covers elastically expandable material and to manufacture the slip covers to smaller dimensions than the upholstered parts they have to cover, so that after inserting the upholstered part in the manufactured slip cover, the latter will adhere perfectly flat and without folds to the upholstered part.
The carrying out of such a sewing operation required considerable experience and skill of the sewing machine operator, since it was necessary that the elastic material of the slip cover was held during the sewing operation by the operator under uniform pretension corresponding to the finished dimensions of the upholstered parts. Nonuniformity of the pretension controlled by the hand of the operator was leading on the finished product to undesirable fold formation.
Auxiliary devices for sewing machines are already known by means of which an elastically stretchable textile material may be sewn to substantially nonstretchable textile material in such a manner to make a uniform arrangement of the stretchable material on the unstretchable material possible. Such an auxiliary device is for instance shown in the U.S. Pat. No. 3,542,262. With such a device it is however not possible to produce seams simultaneously to opposite sides of an elongated slit in the stretchable material. Furthermore, the known auxiliary device requires a cumbersome adjustment of the clamping means thereon so that this device is unsuitable for efficient manufacturing such articles in large series.